The present invention relates to a magneto-resistive sensor reproducing magnetically recorded information and a magnetic storage mounting it. Particularly, it relates to a magneto-resistive sensor having a high output and a fabricating method thereof, a magnetic head using it, and a magnetic storage mounting it.
A magneto-resistive sensor utilizing a magnetoresistance, in which the electrical resistance changes according to changes in an external magnetic field, is well known as an excellent magnetic field sensor, and has been put to practical use as a read sensor for detecting a signal field from a magnetic recording medium which is a main part of a magnetic storage.
The recording density of a magnetic storage has been remarkably improved, and a magneto-resistive sensor has required not only a narrowing of the track width but also high performance in both recording and reproducing properties. With regard to the reproducing properties there has been progress in making high sensitivity by developing an MR head utilizing a magnetoresistance. When the recording density was several Gb/in2, magnetic signals on a recording medium were converted to electric signals by using an anisotropic magnetoresistance (AMR), but a higher sensitivity giant magnetoresistance (GMR) is employed when the recording density becomes higher. In addition, a method bringing the advantage of making high sensitivity (CPP type), in which a detecting current flows nearly in the direction perpendicular to the film plane, has been developed for the requirement of making higher recording density attendant with a narrowing of the gap between the upper shield layer and the lower shield layer (reproducing gap length), and magneto-resistive sensors using CPP-GMR and a tunneling magnetoresistance (TMR) have been reported.
A basic structure of CPP type magneto-resistive sensor will be described. FIG. 1 is a cross-sectional drawing in the track width direction at a position where a magnetoresistive film 3 is placed. The X, Y, and Z axes illustrated in FIG. 1 show the directions of track width, sensor height, and film thickness of the magnetoresistive film, respectively. In the following figures, the X, Y, and Z axes are assumed to be the ones indicating axes identical to the X, Y, and Z axes shown in FIG. 1, respectively. A refill film along track width direction 1 is provided and connected to the wall of the magnetoresistive film 3. A longitudinal bias layer and a side shield layer 5 may not be necessary. Moreover, in FIGS. 1, 2 denotes an upper shield layer and 4 denotes a lower shield layer. FIG. 2 is a cross-sectional drawing in the sensor height direction of a CPP type magneto-resistive sensor cut at the position of line aa′ shown in FIG. 1. In FIG. 2, the right side is an air bearing surface 13 of the magneto-resistive sensor. As the same as the track width direction, the refill film along sensor height direction 6 is provided and connected to the wall of the magnetoresistive film 3. At least the parts of the refill film along track width direction 1 and the refill film along sensor height direction 6 connected to the magnetoresistive film 3 are formed of insulator films.
A narrower track width of the magnetoresistive film 3 has an advantage to make a higher recording density because the size of information recorded in the medium as magnetic signals can be made smaller. Moreover, in order to achieve a high recording density, it is necessary to make the sensor height smaller. This is because sensitivity is improved by placing the magnetoresistive film 3 only in the vicinity of the surface of the air bearing surface 13 which is the place easiest to sense magnetic field, and a magneto-resistive sensor producing a required output is realized even if the track width and the gap between the shields are made smaller to improve the recording density.
However, there are some problems which should be solved to make it smaller. At first, a problem which arises while forming a track will be explained. FIG. 3 is a process flow drawing illustrating a process for forming a track of a CPP type magneto-resistive sensor. After a resist mask 8 with a predetermined size is formed at the region which becomes a read element on the magnetoresistive film 3 deposited on the lower shield layer (FIG. 3(a)), the region except for the read element is etched by an etching technique (FIG. 3(b)). Ion beam etching is generally used in this etching process. After etching, the refill film along track width direction 1 is deposited. As shown in FIG. 3, in some cases, the side shield film or the longitudinal bias layer 5 may be deposited on the refill film along track width direction 1 (FIG. 3(c)). Next, lift-off is carried out using an organic solvent. In the case when the track width of the resist mask 8 is narrower, the resist mask 8 may not be lifted off. Even in the case when lift-off is possible, a fence 9 may be created (FIG. 3(d)). After this process, the upper shield layer 2 which also works as an upper electrode is deposited on the magnetoresistive film 3, but, in the case when the fence is created, a region 12 where the upper shield layer 2 is not deposited is created at the part in the shade of the fence 9. It is expected that contact failure arises caused by the region 12 where the magnetic shield layer 2 is not deposited because of the shade of the fence 9 (FIG. 3(e)), such that conduction may not be obtained between the upper shield layer 2 and the magnetoresistive film 3.
Next, a problem which arises while forming a sensor height will be explained. FIG. 4 is a process flow drawing illustrating a process for forming a sensor height of a CPP type magneto-resistive sensor. After a resist mask 11 with a predetermined size is formed at the region which becomes a read element on the magnetoresistive film 3 deposited on the lower shield layer (FIG. 4(a)), the region except for the read element is etched by an etching technique (FIG. 4(b)). An ion beam etching technique using Ar ions is generally used in this etching process. After etching, the refill film along sensor height direction 6 is deposited (FIG. 4(c)). Next, the resist mask 11 and excess refill film are removed (lift-off) using an organic solvent, but, in the case when the width of the resist mask 11 in the sensor height direction is narrow, the resist mask 11 may not be lifted off. Even in the case when lift-off is possible, a fence 10 may be created (FIG. 4(d)). After this process, the upper shield layer 2 which also works as an upper electrode is deposited on the magnetoresistive film 3, but, in the case when the fence is created, a region 14 where the upper shield layer 2 is not deposited is created at the part in the shade of the fence 10, resulting in contact failure arising in the vicinity of the fence 10 (FIG. 4(e)). Moreover, after this process, the air bearing surface 13 is formed after polishing the sensor height to a predetermined size using a lapping process. However, in the case when there is a region 14 where the upper shield layer 2 is not deposited caused by the shade of the fence 10, conduction may not be obtained between the upper shield layer 2 and the magnetoresistive film 3 (FIG. 4(f)).
As a means to avoid this lift-off failure and creation of a fence, JP-A No. 186673/2004 and JP-A No. 132509/2003 disclose methods in which the resist pattern and fence are removed by carrying out CMP (chemical mechanical polishing method) during the lift-off process. It is described in the previous publications that damage can be avoided by providing a first stopper layer on the magnetoresistive film and a second stopper layer on the refill film because damage may be imparted to the top faces of the magnetoresistive film and the refill film while removing the resist pattern and the fence in the case when CMP is used. These stopper layers are composed of a DLC (diamond like carbon).
The first stopper layer to protect this magnetoresistive film is deposited on the magnetoresistive film. Moreover, a resist mask with a predetermined size is formed on top of it, and then it is etched with the magnetoresistive film. JP-A No. 186673/2004 discloses that only the first stopper layer is etched by reactive ion etching (RIE), and the magnetoresistive film is etched by ion beam etching (IBE). This is because the etching rate of DLC using IBE is significantly lower than that of a metallic material constituting the magnetoresistive film. For instance, in the case when etching was carried out under the condition of an acceleration voltage of 200 V, an ion current of 0.10 A, an RF output of 400 W, and an IBE angle of 10 degrees, the etching rate of a Ni—Fe alloy was 380 A/min and the etching rate of DLC was 80 A/min.
However, there is a case where the height of the resist mask is reduced due to RIE, resulting in lift-off by CMP becoming difficult. This is a problem which becomes particularly apparent when the track width and the sensor height are made smaller. In order to make the track width and the sensor height smaller, it is necessary to make smaller the size of the resist mask in the track width direction and the sensor height direction. In order to realize this, it is necessary to make the height of the resist mask smaller; otherwise, the resist mask falls down, making it impossible to form the pattern. It is known that the limitation of the ratio of the dimension in the track width direction or the sensor height direction to the height of the resist mask (aspect ratio) is 3 to 4. For instance, it is necessary to have a resist mask with a height of 200 nm or less in order to make the dimension of the resist mask in the track width direction or the sensor height direction 50 nm. The height of the resist mask is reduced by using two etching processes which are the process for etching the first stopper layer composed of DLC by using RIE and a process for etching the magnetoresistive film by using IBE, as mentioned above. Actually, the height of the resist mask became about 50 nm when a first stopper layer composed of DLC was deposited on the magnetoresistive film deposited on the lower shield layer, and a resist mask was formed with a height of 200 nm and a dimension in the track width direction of 50 nm, when these two etching processes were applied. After this process, when a refill film and a second stopper layer composed of DLC were formed to protect the refill film and lift-off was carried out by using CMP, 85% of the sensor could not be lifted off and the resist mask could not be removed. This is because lift-off by CMP became difficult due to the height of the resist mask being small.